COST Action TU0904 Integrated Fire Engineering and Response Training school University of Malta, Sliema, 11.-14. April 2012. Scientific project: Reliability of Structures and Risk Assesment to Extreme Loading, Ministry of Science and Tehnology, Croatia NEW NUMERICAL MODELS FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE Neno Torić, PhD student UNIVERSITY OF SPLIT, CROATIA FACULTY OF CIVIL ENGINEERING, ARCHITECTURE AND GEODESY Chair for steel and timber structures
OVERVIEW Introduction Research concept Numerical model for behaviour of steel and concrete structures exposed to fire Experimental research Numerical examples Discussion
INTRODUCTION Development of structural analysis models for predicting fire behaviour Current research is focused on development of structural analysis model comprised of 3D heat transfer model, model for calculating mechanical properties of the cross section and model for structural analysis Development of simplifed model for calculating mechanical properties of the cross section taking into account the additional load dependent strains that occur during heating (creep, transient-creep) Calculation of modified stress-strain curves which implicitly take into account the additional load dependent strains (strain modified curves) 3
RESEARCH CONCEPT Steel steady state test vs. transient state test vs. EC3 steady-state test EC3 transient-state test 4
RESEARCH CONCEPT Concrete steady state test vs. EC2 70 Stress [MPa] 60 50 40 30 20 10 EN1992-1-2-20 C EN1992-1-2] - 230 C EN1992-1-2-400 C EN1992-1-2-500 C EN1992-1-2-600 C EN1992-1-2-700 C EN1992-1-2-800 C STEADY S. TEST - 20 C STEADY S. TEST - 230 C STEADY S. TEST - 400 C STEADY S. TEST - 500 C STEADY S. TEST - 600 C STEADY S. TEST - 700 C STEADY S. TEST - 800 C 0 0 0.004 0.008 0.012 0.016 0.02 0.024 Strain 5
RESEARCH CONCEPT Strain modified curve 6
NUMERICAL MODEL FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE 3D nonlinear heat transfer model, Model for calculating mechanical properties of the cross section Model for structural analysis 5 8 3 6 2 7 3D Bernoulli beam (6 D.O.F.) Cross-section discretization (0,0,0) 1 1 4 2 3 3D Cube element 7
NUMERICAL MODEL FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE Calculation procedure for strain modified curve 8
EXPERIMENTAL RESEARCH Material behaviour 9
EXPERIMENTAL RESEARCH Structure behaviour V Furnace V V 625 1250 625 2500 V Furnace V H V H 625 1250 625 2500 10
EXPERIMENTAL RESEARCH Structure behaviour 8280 2730 2820 2730 HE 320 A Chimney H1 4145 4140 H1 HE 200 A 1955 lvdt3 2730 2820 2730 lvdt4 12 13 14 1590 255 3800 aerated concrete blocks oil burner oil burner oil burner 11
Example 1 Creep model: Dorn/Harmathy V Furnace V=200 kn Steel: S355 V V 625 1250 625 2500 12
Example 1 13
Example 1 14
Example 1 15
Example 1 600 500 400 Temperature [ C] 300 200 100 T_furnace Exp upper flange Exp lower flange 3 Model 0 0 10 20 30 40 50 60 70 80 90 100 110 Time [min] 16
Example 1 Midspan deflection [mm] 50 45 40 35 30 25 20 15 10 5 0 Exp midspan defl EC3 Exp stress-strain curves without creep Exp strain modified curves EC3 strain modified curves 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 115 Time [min] 17
Example 2 Creep model: Dorn/Harmathy V Furnace V=200 kn H=400 kn Steel: S355 V H V H 625 1250 625 2500 18
Example 2 19
Example 2 20
Example 2 21
Example 2 550 500 450 400 T_furnace Exp upper flange Exp lower flange Model Temperature [ C] 350 300 250 200 150 100 50 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 Time [min] 22
Example 2 60 Midspan deflection [mm] 50 40 30 20 Exp midspan defl EC3 Exp stress-strain curves without creep EC3 strain modified curves Exp strain modified curves 10 0 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 Time [min] 23
Example 3 Transient-creep model: Anderberg/Thelandersson K d=20 cm K=20 kn Concrete: C 60/70 Prest. Steel - f y =1600 MPa K K K 2730 2820 2730 8280 24
Example 3 25
Example 3 26
Example 3 27
Example 3 1000 Temperature [ C] 900 800 700 600 500 400 Exp cable T7 Exp cable T8 Exp cable T9 Exp void T10 Exp surface T11 Model T7 Model T8,T9 Model T10 Model T11 T_furnace 300 200 100 0 0 10 20 30 40 50 60 70 80 Time [min] 28
Example 3 220 200 180 160 140 Exp midspan defl LVDT3 Exp midspan defl LVDT4 Exp stress-strain curves EC2 Exp strain modified curves EC2 strain modified curves Deflection (mm) 120 100 80 60 40 20 0-20 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 Time (min) 29
DISCUSSION Application of strain modifed curves in classical structural analysis calculation was presented Validity of the strain modified curves was tested on results of three different experiments conducted on testing of simply supported steel and prestressed concrete elements exposed to high temperatures Numerical results of the three presented examples show good agreement with the experiment by using strain modified curves in terms of predicting the structural stiffness Further research is required to confirm the application of the presented calculation methodology 30
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